Too get rid of ultrasonic noise! Glad you asked
(from "Introduction to Live Sound Reinforcement: The Science, the Art, and the Practice" By Teddy Boyce, p. 132)
You might avoid them, but >99% of recordings don't.
...which contradicts your earlier statement about the recordings being pure DSD. Converted DSD can only be worse than the PCM mix.
Nonsense. If properly used, post tools can improve the sound (EQ, reverb, etc) and of course artists should be free to process sound in any way they see fit. It is THEIR vision.